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Detonation Characteristics of Hydrogen- Oxygen Mixtures

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Detonation Characteristics of Hydrogen- Oxygen Mixtures Detonation Characteristics of Hydrogen- Oxygen Mixtures MORTON P. MOYLE, RICHARD B. MORRISON, and STUART W. CHURCHILL The University of Michigan, Ann Arbor, Michigan Detonation velocities were measured in mixtures of hydrogen and oxygen containing 25 to 75 indicated by LafEtte (14)and Greene (9) mole % hydrogen at initial temperatures from 160' to 580'K. and initial pressures from M to as necessary to attain stable detonation in 2 atm. The measurements were made in a number of tubes of different diameter to permit hydrogen-oxygen mixtures. The probes re- extrapolation to a tube of infinite diameter. Theoretical detonation characteristics were com- quired replacement after 20 to 30 runs. puted for the same range of conditions. The measured and computed velocities are in good The high-temperature runs were made agreement except in rich mixtures and at subatmospheric pressures. Schlieren photographs with the coiled tube in an oven, and the reveal that the detonation wave front is very thin for a stoichiometric mixture but degenerates low-temperature runs with the coiled tube to a complicated zone of interacting shock waves and turbulent combustion as the percentage immersed in 5 gal. of normal propanol in of hydrogen is reduced. The detonation velocity is found to depend only slightly on initial an insulated tank. Dry ice was added to temperature and pressure. The computed pressures behind the detonation and reflected waves the propanol to cool to 200°K. and liquid are roughly proportional to initial pressure and to the reciprocal of the initial temperature. nitrogen to reach lower temperatures. As the result of vigorous stirring, the tempera- The elementary theory of detonation of the elementary theory over a much ture variation within the bath was held was initiated by Riemann (21) with wider range of initial conditions. within rrfr2"K. his work on sound waves and essentially The detonation tube was evacuated and completed b Chapman (5) and Jou- EXPERIMENTAL WORK then filled with premixed oxygen and guet (7). dis elementary theory pos- The experimental equipment for the hydrogen through a mapifold and switch tulates a planar discontinuity in pres- measurement of detonation velocities con- system that kept the ignition circuit open sure, temperature, and composition sisted of six different detonation tubes, a while the filling valve was open. In the moving at sonic velocity with respect mixing and charging system, an ignition low-temperature runs the tube was evac- to the burned ases (the Chapman-Jou- system, and a timing system. uated at room temperature before cooling guet condition? ; chemical equilibrium The characteristics of the detonation to avoid condensation. In both the high- and low-temperature runs the mixture was in the burned gases; no energy, com- tubes are given in Table 1. The five round, straight tubes (A, B, C, D, and E) were not ignited until the pressure indicated on ponent, momentum transfer to the or used to determine the effect of tube dia- a manometer had remained constant for at surroundings; and ideal gas behavior. meter on detonation velocity. Tube F was least 5 min. Analyses of the hydrogen and Subsequent refinements in the theory a 10-in. coil for convenience in tempera- oxygen on a mass spectrograph indicated have been concerned primarily with the ture control for the high- and low-tem- purities greater than 99.5%. The com- structure of the wave. The details of perature experiments. The effect of coiling position of the mixtures were regularly both the classical and the current the- was evaluated by comparison of the velo- determined by the partial-pressure method oretical work are presented in modem cities measured in tubes F and B. Rec- but were periodically checked with a mass books such as Hirschfelder, Curtiss, tangular tube G was used only to obtain spectrograph. and Bird (10)and Courant and Fried- schlieren photographs. All seven tubes The schlieren measurements were made ricks (6) and therefore will not be re- were closed at both ends. by the Topler method ( 1) in a %- by The velocity of the detonation wave was %-in. rectangular tube with a test section peated herein. containing %- by 14-in. windows %-in. Experimental work on detonation has measured with ionization probes. The probes were made by drilling a no. 76 drill thick on two opposite sides. Additional been well reviewed by Lewis and von through a Teflon insert in a stainless steel details concerning the equipment and ex- Elbe (16),and only the immediately sleeve. The probes were threaded into perimental procedures are given in re- pertinent work will be mentioned. The the detonation tubes and adjusted so that ference 18. effect of composition on the detonation the tip was flush with the wall. Each Measurements of detonation velocity velocity of hydrogen-oxygen mixtures probe was connected as a shorting switch were repeated five or more times at the has been investigated extensively, but in the grid of an 884-thyratron tube. The same conditions to check reproducibility. the effects of initial temperature and grid bias of the thyratron tube was ad- All in all over 600 runs were carried out initial pressure have received little at- justed almost to the firing point to obtain at over 100 conditions encompassing a tention. In 1893 Dixon (7) measured maximum sensitivity. When the ionized range of compositions from 25 to 76 mole the detonation velocity in stoichiometric gases behind the detonation front reached % hydrogen for an initial temperature of 298°K. and an initial pressure of 1 atm., mixtures at 283" and over a a probe, the resistance between the probe 373°K. electrode (the drill) and ground (the a range of initial pressures from W to 2 range of pressures from 200 to 1,500 tube wall) fell, and the thyratron fired. atm. for an initial temperature of 298°K. mm. Hg. More recently Bennett and One probe and thyratron started a timer, and compositions from 40 to 76% hydro- Wedaa (2)reported detonation veloci- and another probe and thyratron stopped gen and a range of initial temperatures ties over a pressure range from 10 to it. The time interval was indicated to the from 150" to 477°K. for an initial pres- 400 mm. Hg and Hoelzer and Sto- nearest microsecond. The distances be- sure of 1 atm. and compositions from 41 baugh (11) over a range from 1 to 10 tween the probes and the distance from to 73% hydrogen. The detailed data are atm. the ignitor to the first probe are given in given in reference 18. The averages of the Lewis and Friauf (15) in 1930 and Table 1. The probe locations on tube F repeated runs are presented herein. The Berets, Greene, and Kistiakowsky (3) were on the outside of the coil and were maximum deviation of any individual velocity from the average was less than in 1950 found good agreement between determined before coiling. The distance between the probes was corrected for 1.0% except for a few runs at subatmos- velocities computed from the ele- thermal expansion and contraction of the pheric pressures. mentary theory and experimental values tube in computing the detonation velocity When the velocities measured at atmos- in hydrogen-oxygen mixtures at atmos- at nonambient temperatures. This correc- pheric pressure and 298°K. in the 0.125-, pheric pressure and near-ambient tem- tion was about 0.1% at the extreme 0.250-, 0.375-, 0.909-, and 3.250-in. peratures. The objective of this in- temperatures. The starting distance for all straight tubes were plotted as a function vestigation was to test the predictions the tubes was greater than the distance of initial gas composition, a small but Page 92 A.1.Ch.E. Journal March, 1960 I I 0 0.250" Tube 4000 3.250" Tube 0 Payman I Walls (20) 3600 A Lewis & hiauf (15) o Berets et al. (3) - Theoretical 3200 2800 2400 2000 - 1600 1I 1200 0 20 60 80 1800 40 012345678 % HYDROGEN 1 / D (inches)-' Fig. 2. Detonation velocities at atmospheric pressure and am- Fig. 1. Effect of tube diameter on detonation velocity. bient temperature. definite dependence on tube diameter was velocity is unaffected by coiling or even the National Bureau of Standards tables apparent. Therefore the velocities meas- zigzagging the tube, and the observed (23) were utilized. ured in mixtures containing 34.9, 50.0, and correction is probably due to stretching The pressure, temperature, and equi- 66.7% hydrogen were plotted vs. recipro- the tube in the coiling process rather than librium composition behind the deton- cal tube diameter in Figure 1 as suggested to fundamental effects. ation wave as well as the wave velocity by Kistiakowsky and Zinman (9). The Corrected velocities are presented in all were obtained from the computer. The data of several previous investigators (3, subsequent plots.' further increase in ressure obtained by 4, 7, 15, 20) for atmospheric pressure and temperatures near 298°K. are also in- reflection of the Betonation wave off THEORETICAL COMPUTATIONS cluded. The data appear to lie in parallel a solid wall was also computed with no straight lines indicating that the wall effect further change assumed in composition. The detonation characteristics of hy- The experimental velocities were not is independent of composition in this range. drogen-oxygen mixtures were computed The best set of parallel lines through the measured at exactly the same temper- data of this investigation only was deter- from the elementary theory on an IBM- atures, pressures, and compositions as mined by least squares by the use of the 650 computer over essentially the same those selected for computation. There- method of Ergun (8). These lines are range of initial temperatures, pressures, fore it was necessary to plot and inter- included in Figure 1.
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